The main objective of this work is to develop a suitable fluid dynamic model of a CO2 absorption system using ionic liquids as solvent giving special emphasis in the impact of the viscosity of the solvent on the reactor designing issues such as overall removal capacity, reactor geometry and power required. A very important drawback of ionic liquids is the increase in viscosity during the CO2absorption process which results in a decrease of the overall mass transfer rate and an increase in the power required for pumping and mixing. In order to establish the main mass transfer and hydrodynamic parameters and in particular the impact of the viscosity in the system, a two-dimensional computational fluid dynamic (CFD) simulation was carried out to model a simple gas absorption bubble column with one inlet gas feed. To model the interface tracking, the level set method was used. Meanwhile the laminar and non stationary hypothesis was applied for the liquid and gas phases. The CFD software COMSOL 4.2, which employs the finite elements method to discretized the Navier Stokes and Mass Transfer fluid flow Equations, was used to simulate and analysing the obtained results from simulations. The results show an increase of the overall mean viscosity over the time due to the CO 2diffusion in the liquid, meanwhile the spatial distribution of the viscosity was very homogeneous due to the high mixing capacity of the bubble column. However there was a slight gradient in the bottom of the reactor.